The present invention relates to a honeycomb structure and a method for preparing the same.
The honeycomb structure comprises planar bulk materials of hollow prismatic cells. The heat-resistant honeycomb structure is used in, for instance, peripheral machinery and tools of engines for airplanes, sandwich panels used at portions which are exposed to a high temperature and structural members used in, for instance, airplanes and space machinery and tools which are exposed to high temperature and pressure and have high heat resistance over a long time period in an environment or at a normal service temperature of about 260.degree. C. As base materials for honeycomb structures having a light weight and high mechanical strength and excellent in specific strength with respect to weight, there have conventionally been used, for instance, aluminum foils and kraft paper. As such base materials excellent in heat resistance as well, there have been developed, for instance, those produced by forming metal foils such as stainless steel and titanium foils into honeycomb-like structures and then subjecting the honeycomb structures to brazing process; those prepared by adhering heat-resistant resins such as resol-phenol resins to glass fibers and carbon fibers serving as base materials (fiber reinforced resin honeycomb structure); and those prepared by adhering heat-resistant resins such as resol-phenol resins to synthetic heat-resistant aromatic polyamide paper serving as base materials.
Among them, the fiber reinforced resin honeycomb structure has good specific strength and specific rigidity and therefore it has been used as aircraft parts. If it is used as parts of aircraft engine, it is required to have excellent mechanical strength at high temperature region (120 to 150.degree. C.) and thermoformability into two-dimensional and three-dimensional surface. In order to meet mechanical strength at high temperature region and thermoformability, there has conventionally been used a thermoplastic resin having a glass transition temperature of 250.degree. C. or higher (that is, the resin is softened at a temperature higher than 250.degree. C. which makes the molding of the resin easy) and showing no heat deterioration of mechanical property at a temperature 100.degree. C. lower than the glass transition temperature. However, this thermoplastic resin is solid at an ordinary temperature and does not dissolve in a suitable solvent. Accordingly, it is necessary to heat the resin to 350.degree. C. or higher to convert it to a liquid state before it is used to make a honeycomb structure. For this purpose, a special apparatus for the manufacture of a honeycomb structure is needed, which leads to low efficiency and high cost. Further, the thermoplastic resin itself is expensive.
Moreover, a honeycomb structure comprising a carbon fiber as a base material suffers from radio obstruction problem and therefore, the use thereof is limited.